Abstract
Endophytes are microorganisms that live inside plants and are often beneficial for the host. Kosakonia is a novel bacterial genus that includes several species that are diazotrophic and plant associated. This study revealed two quorum sensing-related LuxR solos, designated LoxR and PsrR, in the plant endophyte Kosakonia sp. strain KO348. LoxR modeling and biochemical studies demonstrated that LoxR binds N-acyl homoserine lactones (AHLs) in a promiscuous way. PsrR, on the other hand, belongs to the subfamily of plant-associated-bacterium (PAB) LuxR solos that respond to plant compounds. Target promoter studies as well as modeling and phylogenetic comparisons suggest that PAB LuxR solos are likely to respond to different plant compounds. Finally, LoxR is involved in the regulation of T6SS and PsrR plays a role in root endosphere colonization.IMPORTANCE Cell-cell signaling in bacteria allows a synchronized and coordinated behavior of a microbial community. LuxR solos represent a subfamily of proteins in proteobacteria which most commonly detect and respond to signals produced exogenously by other microbes or eukaryotic hosts. Here, we report that a plant-beneficial bacterial endophyte belonging to the novel genus of Kosakonia possesses two LuxR solos; one is involved in the detection of exogenous N-acyl homoserine lactone quorum sensing signals and the other in detecting a compound(s) produced by the host plant. These two Kosakonia LuxR solos are therefore most likely involved in interspecies and interkingdom signaling.
Highlights
Endophytes are microorganisms that live inside plants and are often beneficial for the host
LoxR is likely to respond to acyl homoserine lactones (AHLs), whereas PsrR is likely to respond to a plant compound
Two LuxR solos in the recently described genus Kosakonia are reported; LoxR is an SdiA homolog and is able to bind AHLs promiscuously, whereas PsrR belongs to the PAB subfamily that responds to plant compounds
Summary
Endophytes are microorganisms that live inside plants and are often beneficial for the host. We report that a plantbeneficial bacterial endophyte belonging to the novel genus of Kosakonia possesses two LuxR solos; one is involved in the detection of exogenous N-acyl homoserine lactone quorum sensing signals and the other in detecting a compound(s) produced by the host plant. These two Kosakonia LuxR solos are most likely involved in interspecies and interkingdom signaling. SdiA of Escherichia coli and Salmonella can bind and be stabilized by an endogenous signal [16] and respond to exogenous AHLs produced by neighboring bacteria and is involved in virulence in part due to the regulation of transcription of the rck (resistance to killing). QscR from Pseudomonas aeruginosa, on the other hand, is a LuxR solo which responds to the endogenously produced AHL signals by the LasI-LasR system, and its role is to extend the LasI/R regulon [14]
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